Heater cable alarm system

ABSTRACT

In a heater failure alarm system, a current sensor senses the current flow in the heater cable and generates a failure warning signal if there is not current flow when the heater cable is switched on. The current sensing transformer is adapted to be juxtaposed relative to the heater cable and is connected to a self-contained circuit module which closes relay contacts when current flow is not sensed. An alarm switch is mechanically connected to a main power switch for the heater cable and is in series with the relay contacts and an alarm means.

United States Patent [191 I .[111 3,774,189 Brown 1 [451 Nov. 20, 1973[54] HEATER CABLE ALARM SYSTEM 1 3,601,689 8/1971 Kettle! 340/417 [75]Inventor: David 0. Brown, Tulsa, Okla.

Primary Examiner-Thomas B. Habecker [73] Assignee: Sola BasicIndustries, Inc., I Att0mey D vemer Smythe et aL Milwaukee, Wis.

[22] Filed: Sept. 29, 1972 57 ABSTRACT PP 293,346 In a heater failurealarm system, a current sensor senses the current flow in the heatercable and genen [.52] Us. v 340/253 B 340/253 C 340/256 ates a failurewarning signal if there is not current flow 340/417 219/516 when theheater, cable is switched on. The current [51 Int. Cl. cosh 21/00Sensing "ansfmmer is adapted be J'uxlalmsed [58] Field of Search 340/2530 253 B I live the healer cable is a Self" 340 219/510 contained circuitmodule which closes relay contacts when current flow is not sensed. Analarm switch is [56] I R fe Cited mechanically connected to a main powerswitch for UNITED STATES PATENTS the heater cable and is in series withthe relay contacts and an alarm means. 2,355,222 8/1944 Large 340/4173,585,623 6/1971 Laukaitis 340/256 7 Claims, 4 Drawing Figures HEATERCABLE ALARM SYSTEM This invention relates to an equipment and powerfailure alarm and especially to a heating system failure alarm whereinthe failure alarm cooperates with the function of the heating system.

Cable heating systems have been an extremely successful means ofremotely heating pipe lines, conduits, large vessel container, etc.,where conventional heating systems have failed or proved to be tooexpensive. A thermostat with a remotetemperature sensor controls theelectrical power applied. to the electric heating cable to maintain auniform temperature at the remote location and the thermostat may bereadjusted to attain a temperature desired. I-Ieretofore, it has beendifficult to determine whether there has been a failure of the heatingsystem and supply of electrical power. Electrical power can be monitoredby having awatchman observe an indicator, with the indicator beingextinguished in the case of power failure. A failure of the heatingsystem could only be determined if there were a remote temperatureindicator which would need constant observation by a watchman.

One of the objects of the invention is to overcome a serious fault ofthe heretofore known cable heating systems.

Another of the objects of the invention is to provide a failure warningsystem of comparatively low cost and of efficient electrical design.

Still another of the objects of the invention is to provide a failurewarning system that is automatic and does not need constant observation.

Yet another object of the invention is to provide a failure warningsystem that will not yield a fallacious warning when electrical power isintentionally switched off by a thermostat.

According to one aspect of the present invention, a current sensingcircuit senses alternating current flow in a heater circuit by a currenttransformer, rectifies the alternating current, limits the amplitude andintegrates the rectified current and applies it to a relay solenoidcoil. An auxilliary switch is mechanically connected to a main powerswitch for the heater cable which may be controlled by a thermostat. Theauxilliary switch is electrically connected in series with the relaycontacts of the heater failure alarm module, so

that when the heater cable is switched on by the main power switch andno current flow is sensed, the alarm is energized to generate a warningsignal.

Other objects, advantages and features of the present inventionwillbecome apparent from the following description and drawings, which aremerely exemplary.

In the drawings: I

FIG. 1 is an electrical schematic diagram of the heater failure alarmsystem of one embodiment;

FIG. 2 is an electrical schematic diagram of the alarm system of anotherembodiment;

FIG. 3 is a schematic showing of one form of assembly; and

FIG. 4 is an enlarged section of FIG. 3 with the elements turnedrelative to each other.

Where appropriate, the same reference numerals will be used to indicatethe same parts in the various figures.

Referring to FIG. 1, heater cable 11 having leads 11A and 11B isconnected to a source of alternating current power 12 through contactsof power switch 13. A toroidal current transformer 14 is juxtaposedrelative to connected to one lead of rectifyingdiode 15. The other leadofdiode 15 is connected to one lead of a zener diode 16, capacitor 17and relay solenoid coil 18. The other lead of transformer 14 isconnected to one lead of resistor 19 and to the other leads of capacitor17 and relay solenoid coil 18. The other lead of zener diode 16 isconnected to the other lead of the resistor 19.

One terminal 20A of normally closed relay contacts or solenoid-operatedswitch 20 is connected to one terminal 21A of .thermostatically operatedswitch 21 and the other terminal 218 of the switch 21 is connected to aterminal of battery 22 or source of power. A terminal of the battery 22is connected to one terminal of an alarm 23 and the other terminal ofalarm 23 is con-. nected to. terminal 208 of solenoid-operated relayswitch 20. A thermostat 24 is juxtaposed relative to heater cable 12 andis mechanically connected by conventional solenoid-operated means 24A toswitches 13 and 21 to operate them, such mechanical connection beingschematically shown by dotted lines 248. The alarm may be any suitabledevice, such as a light or sound or visual indicator.

In operation, thermostat 24 senses the need for heat and closes powerswitches 13 and auxiliary switch 21, causing alternating current flowthrough the heater cable 12. Auxiliary switch 21 may be part of thethermostat control 24 and 24A. The transformer 14 senses the alternatingcurrent flow and generates an alternating current signal proportional tothe current flow sensed. Diode l5 'rectifies the proportionalalternating current signal and the zener diode 16, in series with theresistor 19, limits the maximum amplitude of the rectifled signal. Thecapacitor 17 integrates the amplitude limited signal and the integratedsignal energizes the relay solenoid coil 18. Energization of coil 18causes relay contacts 20 to open. With the switch 21 closed and contacts20 open, no current can flow from the battery or power source 22 toalarm 23. However, if the thermostat 24 closes the switch 13 and nocurrent flows, due to a fault with the supply of electrical power 12, adefective switch 13 or a defective heater cable 11, the relay solenoidcoil 18 will not be energizedand the contacts 20 will remain closed.There is a complete circuit and the alarm 23 will be energized togenerate a warning signal.

Referring to FIG. 2, a toroidal current transformer 14 has a lead 25 ofthe heater cable 12 wrapped around it.

One lead of transformer 14 is connected to one lead of rectifying diode15. The other lead of diode 15 is connected to one lead of a zener diode16, a capacitor 17 and a relay solenoid coil 18. The other lead oftransformer 14 is connected to one lead of resistor 19 and the otherleads'of the capacitor 17 and the coil 18. The other lead of the diode16 is connected to the other lead of the resistor 19.

With reference to FIG. 2, theamplitude of the signal induced into thetransformer 14 may be varied by wrapping several turns of the lead 25from the heater cable 11 around the transformer 14. Thus, the currentsensitivity may be changed so as to be proportional to the number ofturns wrapped around the coil. In this manner, the same current sensingsystem may be used for heater cables of widely varying currentrequirements.

The alarm and sensing structure can be compactly assembled as may beseen in FIGS. 3 and 4. Also, there may be a plurality of alarm unitsstretched along the cable or pipe.

it will be understood that various details of construction andarrangement of parts may be made without departing from the spirit ofthe invention except as defined in the appended claims.

What is claimed is:

1. In a failure alarm apparatus for an electrical device, thecombination including current sensing means for generating an electricalsignal proportional to the current sensed, rectifying means forrectifying said current proportional electrical signal, voltage limitingmeans for limiting the maximum amplitude of said rectified currentproportional signal, capacitor means for integrating said limited,rectified current proportional signal, relay means for operating a setof electrical contacts when energized by said integrated, limited andrectified current proportional signal, and alarm means for producing awarning signal, wherein said alarm means is connected to the electricalcontacts of said -relay so that a warning signal is produced when achange in current flow is sensed by said current sensing means.

2. In a failure warning apparatus as claimed in claim 1 wherein saidvoltage limiting means comprises a zener diode in series with aresistor.

3. in a failure warning apparatus as claimed in claim 1 wherein thewarning signal is produced when the current flow sensed is below apredetermined level.

4. In an electrical apparatus, the combination including a supply ofelectrical power, electrical equipment, a first switch interconnectingsaid electrical equipment and said supply of electrical power, currentsensing means for sensing the flow of current to said electricalequipment, a second switch operated by said current sensing means, athird switch mechanically connected to said first switch wherein saidsecond and third switches are connected in series, and alarm means forproducing a warning signal, operated by said second and third seriallyconnected switches, wherein when said first switch is interconnectingsaid electrical equipment and said supply of electrical power and saidcurrent sensing means does not sense the flow of current, said secondand third switches operate said alarm means to generate a warningsignal.

5. An apparatus as claimed in claim 3 wherein said current'sensing meanscomprises a current transformer means for inductively sensing the flowof current in an electrical circuit and producing an electrical signalproportional to the current sensed, rectifying means for rectifying saidcurrent proportional electrical signal, voltage limiting means forlimiting the maximum amplitude of said rectified current proportionalsignal, capacitor means for integrating said limited, rectified currentproportional signal, and solenoid means for operating said second switchwhen energized by said integrated, limited and rectified currentproportional signal.

6. The apparatus of claim 5 including a thermostat mechanicallyconnected to said first and third switches, wherein said electricalequipment is an electrical heater and said thermostat senses thetemperature of the electrical heater and operates the first switch tomaintain a relatively constant temperature.

7. In a heater failure alarm for a heater cable energized by alternatingcurrent, the combination including a current transformer adapted to bejuxtaposed relative to a heater cable for inductively sensing the flowof current in the heater cable and producing an alternating currentproportioned electrical signal which is proportional to the currentsensed, a diode rectifier for converting said alternating currentporportional electrical signal to a direct current signal, zener diodemeans for limiting the maximum amplitude of said direct current signal,a capacitor for integrating said limited direct current signal, alarmmeans for producing a warning nal.

1. In a failure alarm apparatus for an electrical device, thecombination including current sensing means for generating an electricalsignal proportional to the current sensed, rectifying means forrectifying said current proportional electrical signal, voltage limitingmeans for limiting the maximum amplitude of said rectified currentproportional signal, capacitor means for integrating said limited,rectified current proportional signal, relay means for operating a setof electrical contacts when energized by said integrated, limited andrectified current proportional signal, and alarm means for producing awarning signal, wherein said alarm means is connected to the electricalcontacts of said relay so that a warning signal is produced when achange in current flow is sensed by said current sensing means.
 2. In afailure warning apparatus as claimed in claim 1 wherein said voltagelimiting means comprises a zener diode in series with a resistor.
 3. Ina failure warning apparatus as claimed in claim 1 wherein the warningsignal is produced when the current flow sensed is below a predeterminedlevel.
 4. In an electrical apparatus, the combination including a supplyof electrical power, electrical equipment, a first switchinterconnecting said electrical equipment and said supply of electricalpower, current sensing means for sensing the flow of current to saidelectrical equipment, a second switch operated by said current sensingmeans, a third switch mechanically connected to said first switchwherein said second and third switches are connected in series, andalarm means for producing a warning signal, operated by said second andthird serially connected switches, wherein when said first switch isinterconnecting said electrical equipment and said supply of electricalpower and said current sensing means does not sense the flow of current,said second and third switches operate said alarm means to generate awarning signal.
 5. An apparatus as claimed in claim 3 wherein saidcurrent sensing means comprises a current transformer means forinductively sensing the flow of current in an electrical circuit andproducing an electrical signal proportional to the current sensed,rectifying means for rectifying said current proportional electricalsignal, voltage limiting means for limiting the maximum amplitude ofsaid rectified current proportional signal, capacitor means forintegrating said limited, rectified current proportional signal, andsolenoid means for operating said second switch when energized by saidintegrated, limited and rectified current proportional signal.
 6. Theapparatus of claim 5 including a thermostat mechanically connected tosaid first and third switches, wherein said electrical equipment is anelectrical heater and said thermostat senses the temperature of theelectrical heater and operates the first switch to maintain a relativelyconstant temperature.
 7. In a heater failure alarm for a heater cableenergized by alternating current, the combination including a currenttransformer adapted to be juxtaposed relative to a heater cable forinductively sensing the flow of current in the heater cable andproducing an alternating current proportioned electrical signal which isproportional to the current sensed, a diode rectifier for convertingsaid alternating current porportional electrical signal to a directcurrent signal, zener diode means for limiting the maximum amplitude ofsaid direct current signal, a capacitor for integrating said limiteddirect current signal, alarm means for producing a warning signal whenswitched on, a relay for switching said alarm means when energized bysaid limited direct current signal to prevent said alarm from producinga signal.